RSV infections are a major cause of respiratory tract disease in humans, cattle, sheep and goats (Stott and Taylor, 1985). The virus is classified within the Pneumovirus genus of the Paramyxoviridae. Human respiratory syncytial virus (HRSV) is the most important causative agent of bronchiolitis and pneumonia in infants and young children. Approximately 100,000 children are hospitalized each year in the USA as a result of RSV infection. A vaccine against the virus is not available and development of a vaccine is third--subsequent to Malaria and Human Immunodeficiency Virus--on the priority list of the World Health Organization. In cattle, respiratory disease is one of the most frequently recorded diseases. Recent reports indicate that respiratory disease can account for up to 60% of morbidity and for around 60% of mortality in feedlot cattle (Healy et al., 1993, Edwards, 1989). Bovine respiratory syncytial virus (BRSV) infections are the major cause of respiratory disease in calves resulting in high economic losses.
Because different antigenic subgroups are described for HRSV and BRSV (Johnson et al., 1987, Furze et al., 1994), it is important to monitor the prevailing subgroups in a population to choose a candidate vaccine of the right subgroup(s)
The virus has two major surface glycoproteins: the attachment protein G and the fusion protein F. The G protein is unique for RSV, it is highly variable between HRSV subgroups (53% amino acid homology; Johnson et al., 1987), or between HRSV and ungulate RSV (30% amino acid homology; Lerch et al., 1990). However, within the subgroups the amino acid homology is much larger (80% or more within several HRSV-A strains; Cane et al., 1991), 90% or more within several HRSV-B strains (Sullender et al., 1991) and 90% or more within four BRSV strains (Mallipeddi and Samal, 1993a). The G protein shares neither sequence nor structural homology with other attachment proteins of other Paramyxoviruses (Satake et al., 1985, Wertz et al., 1985). In contrast to the attachment proteins of other paramyxoviruses, G is shorter and lacks hemagglutination or neuraminidase activity. RSV-G is a type II membrane protein and contains about 60% carbohydrate by weight. Approximately 20% of the carbohydrate moieties are N-linked carbohydrates and 80% are O-linked carbohydrates which are linked to the unusually high number of hydroxy amino acids in the protein.
A number of diagnostic assays (reviewed by Welliver, 1988) are available for the detection of RSV. However, these assays are based on whole virus or complete proteins that do not (effectively) discriminate between subgroups of HRSV nor between different RSV types. Because the F protein is highly conserved between all RSV types, a discriminating assay is hard to design based on protein F and should therefore include at least a part of the more variable G protein.
Empirical methods to determine the immunodominant site on BRSV-G and HRSV-G showed that the immunodominant site of the peptide was located within the C-terminal half of this peptide (residues 174-188; Norrby et al., 1987). It has been suggested that a 15-residue peptide (residues 174-188) could be used for subtype-specific site-directed serology (Akerlind-Stopner et al., 1990, Norrby et al., 1987).
The use of peptides as antigens in serological diagnosis of infections has gained interest, because peptides are cheap and easy to produce in a reproducible manner. However, the use of peptides in routine diagnosis has so far been limited due to lack of sensitivity.